Provided by: libbobcat-dev_5.11.01-1_amd64 
NAME
FBB::HMacBuf - Computes HMAC Message Digests from information inserted into a std::ostream
SYNOPSIS
#include <bobcat/hmacbuf>
Linking option: -lbobcat -lcrypto
DESCRIPTION
FBB::HMacBuf objects are std::streambuf objects that can be used to initialize
std::ostream objects with.
All information inserted into such a std::ostream is used to compute a message HMAC from.
All the message digest algorithms defined by the OpenSSL library that can be selected by
name may be used in combination with HMacBuf objects.
The following message hmac algorithms are currently supported: mull, md2, md5, sha, sha1,
sha224, sha256, sha384, sha512, dss, dss1, ecdsa, mdc2, ripemd160. These very names are
the ones to use to select the particular digest algorithm for the class’s constructor,
below. It is quite possible that future releases of the openssl library will support
additional message digest algorithms. The header file openssl/evp.h lists all available
hmac algorithms (in that file look for EVP_MD *EVP_: a message digest algorithm
immediately follows the 2nd underscore. E.g., const EVP_MD *EVP_md4(void) which refers to
the md4 message digest algorithm).
NAMESPACE
FBB
All constructors, members, operators and manipulators, mentioned in this man-page, are
defined in the namespace FBB.
INHERITS FROM
std::streambuf
CONSTRUCTORS
o HMacBuf(std::string const &key, char const *type, size_t bufsize = 1024):
This constructor initializes the streambuf, setting it up for the message digest
algorithm specified with type. The message hmac algorithms specified in the
DESCRIPTION section may be used here. E.g., to use the sha256 algorithm specify
"sha256".
The constructor’s first argument defines the key to be used when computing the HMAC
message digest.
The bufsize argument specifies the internal buffer used by HMacBuf to store
incoming characters temporarily. The provided default argument should be OK in all
normal cases.
Copy and move constructors (and assignment operators) are not available.
OVERLOADED OPERATOR
o std::ostream &operator<<(std::ostream &out, HMacBuf const &hmacbuf):
The insertion operator is a free function defined in the namespace FBB. It inserts
a hash value as a series of hexadecimally displayed values into the provided
ostream. See the example below for an illustration.
MEMBER FUNCTIONS
All members of std::streambuf are available, as FBB::HMacBuf inherits from this class.
o void eoi():
This member completes the message digest computation. It is needed as the HMacBuf
object has no external means for deciding whether all information to compute the
digest for has yet been received or not. Alternatively, the eoi manipulator can be
inserted into the stream computing the message digest (see below) The general
approach for computing a message hmac is therefore:
create a HMacBuf object
use it to create a std::ostream object
insert information into the ostream object
call the HMacBuf object’s eoi() member or insert eoi into the ostream
object
obtain/process the hash value from the HMacBuf object.
o std::string const &hash() const:
This member returns the hash value computed by the HMacBuf object. Its value is
only defined after having called close(). The hash value is returned in a
std::string object. This string’s length() member contains the number of characters
used by the hash value, and its data() member refers to the hash value’s
characters. Note that a hash value’s character value may be 0 (not to be confused
with ’0’).
o void reset():
This member reinitializes the message hmac computation. One a message hmac has been
computed for, say a stream streamA this member can be called after which the hmac
for a stream streamB can be computed using the same HMacBuf object.
o void eoi():
This member can be called to complete the message digest computation. Instead of
calling this member the eoi manipulator (see below) can be used.
MANIPULATOR
o FBB::eoi:
The eoi manipulator can be inserted into the ostream to complete the digest
computation. If it is inserted into a plain std::ostream nothing happens.
EXAMPLE
#include <iostream>
#include <ostream>
#include <cstring>
#include <iomanip>
#include <bobcat/exception>
#include "../hmacbuf"
using namespace std;
using namespace FBB;
int main(int argc, char **argv)
try
{
if (argc < 3)
throw Exception{} << "Arg1: key, arg2: digest method required";
string key(argv[1]);
HMacBuf hmacbuf{ key, argv[2] };
ostream out(&hmacbuf);
string hw{ "hello world\n" };
out << hw << eoi;
cout << ">" << hmacbuf << "<" << endl;
// hmacbuf.reset();
// out.write(hw.c_str(), hw.length()) << eoi;
// cout << ">" << hmacbuf << "<" << endl;
}
catch(exception const &err)
{
cout << err.what() << endl;
return errno;
}
FILES
bobcat/hmacbuf - defines the class interface
SEE ALSO
bobcat(7), digestbuf(3bobcat), std::streambuf
BUGS
None reported
BOBCAT PROJECT FILES
o https://fbb-git.gitlab.io/bobcat/: gitlab project page;
o bobcat_5.11.01-x.dsc: detached signature;
o bobcat_5.11.01-x.tar.gz: source archive;
o bobcat_5.11.01-x_i386.changes: change log;
o libbobcat1_5.11.01-x_*.deb: debian package containing the libraries;
o libbobcat1-dev_5.11.01-x_*.deb: debian package containing the libraries, headers
and manual pages;
BOBCAT
Bobcat is an acronym of `Brokken’s Own Base Classes And Templates’.
COPYRIGHT
This is free software, distributed under the terms of the GNU General Public License
(GPL).
AUTHOR
Frank B. Brokken (f.b.brokken@rug.nl).